Arctus is a non-combatant Autobot engineer in to the secure facility used to launch the AllSpark into space.
Arctus concerns himself with the tangible reality around him, he has little grasp of weighty philosophical issues; something either is or is not, action should be taken, or not taken. Hand-wringing will not change an unpleasant necessity.
Arctus's name and non-combatant status seems to imply he was the architect of the launch facility.
Arctus could not understand why Optimus Prime hesitated to give the command to launch the AllSpark into space.
When a Decepticon combat drone attacked the facility, Arctus stayed in launch control and did not join the fighting.
While Optimus Prime fought the drone, the Allspark was sent into space. Arctus apparently initiated the launch rather than wait and determine who won, though this is not stated explicitly.
This story is incompatible with the events of the IDW Movie prequel.